Make Your Own Expression

Make Your Own Expression

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Geometry Expressions can calculate output as expressions, but you can also define and add your own expressions to a drawing.

From this model,

 

  1. Select the two points A and D.
  2. Calculate the distance between them as a symbolic output.
  3. Select the expression youve just output.
  4. Right click and then select Output Properties > Show Name > Yes

To the left of the arrow, the name zn appears. (Because you may have created one or more of these already while exploring, we cant predict the exact number in the subscript.) This is the symbol the application assigns by default as the name of the expression.

  1. Select the two points D and C, and repeat the previous three steps to get a second expression, this one named zn+1. (Subscripts increase by one each time the symbol they apply to is reused.)

Using these names, you can make an expression of your own to refer to these distances. For example, you can calculate the ratio of the two lengths.

  1. In the Draw palette, choose the Expression tool.

draw_expr 

  1. Click in the drawing where you want to put the expression. The expression appears as a 0, selected for overwriting. To replace the zero, enter: z[n]/z[n+1]

(Square brackets indicate subscripts. Replace the n and n+1 with the subscripts for your own named expressions.)

  1. The expression is calculated and displayed.